In semiconductor substrate processing it is often necessary to provide carefully blended processing fluids to a processing chamber in which semiconductor wafers, photomasks, and other similar products are being treated or processed. Blended processing fluids may, for example, include mixtures of hydrogen peroxide with sulfuric acid, ammonium hydroxide, water and other processing fluids. Similarly, hydrofluoric acid may need to be blended with water, acidic acid, nitric acid, phosphoric acid or other processing fluids.
Because of the relatively small size of semiconductor processors and the small number of articles typically processed at one time, the amounts of such processing fluids are relatively small. This requires that the metering of various constituents be done accurately to achieve the desired blend. Additionally, it is of utmost concern that the fluids be blended in a manner which does not add undesired contaminants to the processing fluids. Such contaminants can cause serious loss of wafer yields.
The desired blending of process fluids is particularly of significance in processing where the same group of chemicals may be used in varying processing steps in different concentrations and or combinations. Previously it has been difficult to achieve repeatable accurate blending of processing fluid components from one processing run to the next. Each time the processing fluid constituents are mixed there is a chance for variability due to operator error and simple inability to accurately control the amounts of chemicals being combined to produce the desired blended processing fluid. Thus the semiconductor industry has experienced a keen need for processing equipment which can be stocked with several different processing fluids and then provide automated blending of these fluids without operator judgement and manual control. Previous systems were unable to achieve the desired degree of blending accuracy and repeatability.